1. Field of the Invention
This invention relates to a method of manufacturing a glass optical part, and in particular to a method of obtaining an optical part by pressing glass in its molten state from the opposite sides thereof by shaping mold members while causing the glass to flow down.
2. Related Background Art
As methods of obtaining an optical part from a glass blank by press molding, there are the so-called reheat press method and direct press method.
In the reheat press method, a glass blank similar in shape to a final molded article is once formed, and this blank is contained in a shaping mold apparatus and heated and pressed to thereby obtain a final molded article corresponding to the shape of a cavity formed by the mold member of the mold apparatus.
In the direct press method, molten glass is introduced into a shaping mold apparatus and pressed to thereby directly obtain a final molded article corresponding to the shape of a cavity formed by the mold member of the mold apparatus.
Now, the glass blank used in the above-described reheat press method should preferably be good to some degree in shape accuracy and surface accuracy and therefore, the glass blank is ground and polished in some cases to obtain a final product of predetermined accuracy. However, this requires time and labor for grinding and polishing and thus, in some cases, the above-described direct press method is utilized to manufacture said glass blank.
As the direct press method, there is a system as described, for example, in Japanese Laid-Open Patent Application No. 63-248727 and Japanese Laid-Open Patent Application No. 1-133948 wherein molten glass is sandwiched from the opposite sides thereof by the use of a pair of shaping mold members horizontally opposed to each other while the molten glass is caused to flow down from a nozzle, and the glass is cooled and cured in a cavity thus formed, thereby obtain a molded article of a predetermined shape. In this system, a ring-like cutting member is disposed around the optical surface shaping surface of one of the shaping mold members and this cutting member is moved forward simultaneously with or after the forward movement of the mold members to thereby cut and remove the protruding portion of the glass and form an optical part of a desired shape. This system is preferable in that an optical part can be obtained without the cutting traces of the flowing-down molten glass remaining on the optical surface.
However, in the above-described system, when the glass is cut by the ring-like cutting member, dust may be created by the contact of the cutting member with the other mold member and such dust may adhere to the shaping surfaces of the mold members after the parting of the molded article and may further adhere to the glass surface which will provide the optical surface during the next press, thereby deteriorating the optical characteristic of the molded article.
Further, as described above, the ring-like cutting member contacts with the other mold member and therefore is short in life and frequent replacement thereof is necessary, and this has hampered improvements in the manufacturing efficiency.